"While a motive was not clear, small armed anarchist or domestic terrorist groups have set off attacks in Greece for decades. They usually target official buildings, banks or symbols of state power with small bombs or incendiary devices and rarely cause injuries.

"Police said initial information indicated three people had been inside the van. The hooded assailants forced the building's two security guards out at gunpoint before reversing the van into the front entrance, smashing the door.

"They then triggered an incendiary device inside the van that police said appeared to have consisted of camping gas canisters and several containers of gasoline."

Reuters provides a bit of background saying while anarchists have carried out attacks since 1974, social tensions have been rising in the country because of the tough austerity measures imposed on Greece by the bailout deal it struck with the E.U.

Reuters adds:

"Branches of Macdonald's, Citi and Starbucks in Athens have been set on fire by protesters and militants in the past using petrol bombs or gas canisters.

"The attacks usually take place at night and there have rarely been injuries, but three bank staff suffocated in May 2010 when protesters set their branch on fire during a protest march in central Athens.

"The assault on Microsoft is a new headache for big multi-nationals in Athens already considering quitting the debt-ridden country because of unpaid bills, falling revenues and the prospect that Greece might be forced to leave the euro."

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.